In recent years, optical topological insulators have become the focus of condensed matter physics research. They have energy band structures protected by topology and provide many novel mechanisms for light field regulation, such as one-way transmission with backscattering suppression, directional selective transmission with pseudospin vector locking, high-dimensional light field regulation, etc. They are expected to be applied to on-chip topological waveguides and photonic integrated circuits, and have great application prospects in the field of modern optical communications.
Gao Yongfeng, associate professor of the Department of Optoelectronic Information Science and Engineering of the School of Mechanical Engineering of Jiangsu University, proposed that the topological mediocre photonic crystals are composed of silicon dielectric columns in the air background, and the topological non mediocre photonic crystals are composed of pores above the silicon dielectric substrate. There are topological phase transitions and energy band reversals between the two types of photonic crystals, and a box type composite structure composed of topological mediocre and non mediocre photonic crystals is constructed (Figure 1). In the modal discrete spectrum of the box type composite structure, there are topological boundary states and topological angle states in the band gap of the body shape (Figure 2). It is found that although the light in the body band gap cannot be transmitted in the body region, the topological boundary states in the body band gap can be transmitted along the boundaries of different topological regions, and the topological angle states will be localized at the corners of the composite structure. Figure 3 shows the electric field distribution of body state, boundary state and angle state.
Recently, the work was published on Physical Review A, a journal of Nature Index, under the title of "Corner states in second order two dimensional topologic photo crystals with reversed materials". Associate Professor Gao Yongfeng is the corresponding author of the paper, Jin Mengcheng, a master of optical engineering, is the first author of the paper, Lin Haozhe, He Yihan and Professor Chen Mingyang are co authors of the paper, and the School of Mechanical Engineering of Jiangsu University is the only signatory of the paper.
This research achievement has been granted a Chinese invention patent (patent No.: ZL202111296850.7). This work was supported by the Zhenjiang Key Laboratory of Advanced Sensing Materials and Devices (No. SS2018001), the Jiangsu Postgraduate Research and Practice Innovation Project (KYCX22_3628) and the Jiangsu University Undergraduate Practice Innovation Training Project (202110299419X, 202110299423X).
This work realizes the topological phase transition and energy band inversion by exchanging the materials of the photonic crystal medium column and the background, which provides a new idea for realizing high-order topological photonic insulators. Two kinds of box type composite structures are designed by using topological ordinary and non ordinary photonic crystals. Topological boundary states and angular states are observed at the boundary and corner of the composite structure, which further reveals the formation mechanism of angular states and analyzes the robustness of angular states to structural defects. This work provides a new platform for topological optics research, and will have an important guiding significance for the design of optical integrated devices and their applications in optical communication.
Thesis: Meng Cheng Jin, Yong Feng Gao *, Hao Zhe Lin, Yi Han He, and Ming Yang Chen “Corner states in second-order two-dimensional topological photonic crystals with reversed materials”PHYSICAL REVIEW A 106, 013510 (2022)
Link: https://link.aps.org/doi/10.1103/PhysRevA.106.013510
DOI: https://doi.org/10.1103/PhysRevA.106.013510
